This invention relates to a method for determining the presence of selected immunochemically responsive substances such as antibodies or antigens in body fluids. These selected substances will be referred to hereinafter as analytes.
The determination of such analytes provides much useful medical information. For example, pregnancy testing, syphilis testing and blood factor testing are all now done by conventional immunochemical methods. Most of these methods involve a visual inspection for the formation of precipitated or agglutinated antigen-antibody complexes. These methods sometimes require several replications at different reagent ratios to insure accuracy and also require an individual visual inspection for each test result. Use has also been made of radioactive and fluorescent tags to avoid the subjective visual determination. However, these methods sometimes have problems either in the use of expensive or transient tags, or in sensitivity or in safety and handling of radioactive materials. The method of this invention uses immune reagents tagged with particles such as magnetic materials which are safe to handle and which can be detected readily with highly sensitive and readily available electronic equipment. This method is readily adaptable to automated or semi-automated operation.
The use of magnetic particles in serological testing is known, but prior to this invention the magnetic particles have been used only to remove or sequester various components from a liquid sample. For example, U.S. Pat. Nos. 4,018,886 and 3,970,518, teach the use of magnetically active particles to collect selected proteins, followed by cleaving the proteins from the magnetic particles and a visual examination for precipitated proteins. Hersh et al., U.S. Pat. No. 3,933,997, teaches the use of magnetic particles to concentrate radioactive tags on a test substance.
None of the references teach the use of magnetic detection to obtain the desired result.